mod_ssl: Make the size of the per-dir-reneg request-body buffer

configurable, by popular demand:

* modules/ssl/ssl_private.h: Define DEFAULT_RENEG_BUFFER_SIZE.
  (SSLDirConfigRec): Add nRenegBufferSize field.

* modules/ssl/ssl_engine_config.c (ssl_cmd_SSLRenegBufferSize): New
  function.
  (ssl_config_perdir_create, ssl_config_perdir_merge): Handle
  nRenegBufferSize.

* modules/ssl/ssl_engine_io.c (ssl_io_buffer_fill): Take max buffer
  size as an argument rather than compile-time constant.

* modules/ssl/ssl_engine_kernel.c (ssl_hook_Access): Pass
  nRenegBufferSize to ssl_io_buffer_fill.

* modules/ssl/mod_ssl.c (ssl_config_cmds): Add SSLRenegBufferSize.

PR: 39243


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@726109 13f79535-47bb-0310-9956-ffa450edef68